Allergies linked to baby's birthplace, gut bugs

NEW YORK (Reuters Health) - Where and how a baby is born might affect its chances of getting allergies and asthma growing up, suggests a new study.

Researchers found that babies were more likely to harbor a certain kind of bacteria in their intestines if they were born in the hospital, and especially by cesarean section -- and those gut bugs were tied to a kid's chances of later getting allergies or asthma.

"Our message is not that mode nor place of delivery (decisions) should be based on the potential risks on developing allergic diseases," study author John Penders, from Maastricht University in the Netherlands told Reuters Health in an email.

But, researchers said, it's one more topic to add to a growing list of potential culprits behind the recent increase in asthma and allergies in kids.

The study included about 2,700 babies who were followed until they were seven years old.

One month after birth, the researchers tested fecal samples from infants, looking to see whether their intestines were hosting a few specific species of bacteria, such as Escherichia coli and Clostridium difficile.

When kids were older, Penders' team asked parents to report how often the children wheezed and needed asthma medications, and whether they had recently had an itchy rash called eczema. Kids also got blood tests to see if they had warning signs of food or pet allergies.

The researchers found that C. difficile, a type of bacteria known to spread in hospitals, was most commonly seen in the intestines of babies born by cesarean section. Forty-three percent of them harbored C. difficile in their feces, compared to 27 percent of babies born vaginally in the hospital and 19 percent of those born at home.

Researchers said that while babies born vaginally get their first gut bacteria from their moms -- in the birth canal and through other direct contacts -- C-section babies are first exposed to bacteria on doctors' and nurses' skin, or from other places in the delivery room.

And that early first exposure to bacteria, they found, could have later implications. Kids who tested positive for C. difficile as babies were twice as likely to have asthma at age six or seven, and were also more likely to have eczema or a food "sensitization."

In all, about seven percent of kids had asthma, close to 22 percent had the warning signs of a food allergy and 12 percent recently had eczema.

Gut microbes are known to regulate and influence important aspects of immune functioning throughout body.

Penders and his colleagues proposed in the Journal of Allergy and Clinical Immunology that a particular balance of gut microbes may predispose certain kids to asthma and allergies -- although their study can't prove that one causes the other.

Peter Bager, who has studied delivery and allergy risks at the Statens Serum Institut in Copenhagen, Demark, said that would fit in with the "hygiene hypothesis" -- which posits that kids have more allergies these days because they're too clean.

Having a skewed mix of gut bacteria species early on, especially lacking a diverse range of bacteria, "reduces the early stimulation of the immune system," which could lead to more allergies later on, said Bager, who was not involved in the new research.

But Dr. Ruchi Gupta, an allergy researcher from Children's Memorial Hospital in Chicago who also was not involved in the study, said it's hard to interpret too much from the findings. "There are so many factors that go into a child's development of allergies and asthma," she told Reuters Health.

"Although I think the results are interesting, I think they're a first step," she said, adding that more investigation is needed into the possible link between gut microbes and allergies.

"We cannot conclude that this specific bacterium (C. difficile) is the cause of the increased risk on allergies and asthma," Penders added. "The microbiota contains thousands of different species and we only measured a few of them."